This invention is generally directed to toner and developer compositions and processes thereof, and more specifically, the present invention is directed to developer and toner compositions and processes thereof containing a pigment, optionally a charge control agent and coalesced submicron particles, wherein the submicron particles are composed of a polyester core encapsulated by a styrene-acrylic acid resin shell.
In embodiments, the present invention is directed to the preparation of submicron particles comprised of a polyester core encapsulated by a styrene-acrylic acid resin by seed polymerization process, and the economical in situ chemical preparation of toners by the emulsion aggregation/coalescence process without the utilization of the known pulverization and/or classification methods, and wherein in embodiments toner compositions with an average volume diameter of from about 1 to about 25, and preferably from 1 to about 10 microns, and narrow GSD of, for example, from about 1.16 to about 1.26 as measured on the Coulter Counter can be obtained. The resulting toners can be selected for known electrophotographic imaging, printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally toner additives like a charge control agent or additive in an aqueous mixture containing an ionic surfactant in an amount of from about 0.5 percent (weight percent throughout unless otherwise indicated) to about 10 percent, and shearing this mixture with a latex of submicron composite particles comprised of a polyester core with a shell of a copolymer of styrene acrylate-acrylic acid of from, for example, about 0.01 micron to about 2 microns in volume average diameter, and which composite particles are obtained from the seed polymerization of monomers, such as acrylic acid, styrene and or methacrylates, a polymerization initiator and a polyester submicron particle comprised of, for example, poly(propylene-terephthalate) or poly(propoxylated bisphenol A-fumarate), in an aqueous solution containing a counterionic surfactant in amounts of from about 1 percent to about 10 percent with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant in amounts of from about 0 percent to about 5 percent, thereby causing a flocculation of composite particles, pigment particles and optional charge control agent, followed by heating at about 5 to about 40.degree. C. below the shell Tg and preferably about 5 to about 25.degree. C. below the shell Tg while stirring of the flocculent mixture which is believed to form statically bound aggregates of from about 1 micron to about 10 microns in volume average diameter comprised of modified polyester resin, pigment and optionally charge control particles, and thereafter heating the formed bound aggregates about above the Tg (glass transition temperature) of the composite particle. The size of the aforementioned statistically bonded aggregated composite particles can be controlled by adjusting the temperature in the below the resin Tg heating stage. Thus, for example, an increase in the temperature causes an increase in the size of the aggregated particle. This process of aggregating composite particles and pigment particles is kinetically controlled, that is the temperature increases the process of aggregation. The higher the temperature during stirring the quicker the aggregates are formed, for example from about 2 to about 10 times faster in embodiments, and the latex submicron particles are picked up more quickly. The temperature also controls in embodiments the particle size distribution of the aggregates, for example the higher the temperature the narrower the particle size distribution, and this narrower distribution can be achieved in, for example, from about 0.5 to about 24 hours and preferably in about 1 to about 3 hours time. Heating the mixture about above or in embodiments equal to the resin Tg generates toner particles with, for example, an average particle volume diameter of from about 1 to about 25 and preferably 10 microns. It is believed that during the heating stage the components of aggregated composite particle shell fuse together to form composite toner particles. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.TM.), utilizing a high shearing device, such as a Brinkmann Polytron, microfluidizer or sonicator, thereafter shearing this mixture with a latex of suspended particles of monomers of acrylic acid and styrene, and which latex also contains a polyester resin, and which particles are, for example, of a size ranging from about 0.01 to about 0.5 micron in volume average diameter as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate (for example NEOGEN R.TM. or NEOGEN SC.TM.), and a nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy)ethanol (for example IGEPAL 897.TM. or ANTAROX 897.TM.), thereby resulting in a flocculation, or heterocoagulation of the formed composite particles comprised of a polyester with a shell thereover of a copolymer of styrene-acrylic acid with the pigment particles; and which, on further stirring for about 1 to about 3 hours while heating, for example, from about 35.degree. to about 45.degree. C., results in the formation of statically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II), where the size of those aggregated particles and their distribution can be controlled by the temperature of heating, for example from about 5.degree. to about 25.degree. C. below the resin Tg, and where the speed at which toner size aggregates are formed can also be controlled by the temperature. Thereafter, heating from about 5.degree. to about 50.degree. C. above the resin Tg provides for particle fusion or coalescence of the polymer and pigment particles; followed by optional washing with, for example, hot, for example at a temperature of from about 50.degree. to about 90.degree. C., water to remove surfactant, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to about 20, and preferably 12 microns in average volume particle diameter. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present.
While not being desired to be limited by theory, it is believed that the flocculation or heterocoagulation is caused by the neutralization of the pigment mixture containing the pigment and ionic, such as cationic, surfactant absorbed on the pigment surface with the resin mixture containing the polyester resin particles and anionic surfactant absorbed on the resin particle. This process is kinetically controlled and an increase of, for example, from about 25.degree. C. to about 45.degree. C. of the temperature increases the flocculation, increasing from about 2.5 to 6 microns the size of the aggregated particles formed, and with a GSD charge of from about 1.39 to about 1.20 as measured on the Coulter Counter; the GSD is thus narrowed down since at high 45.degree. C. to 55.degree. C. (5.degree. C. to 10.degree. C. below the resin Tg) temperature the mobility of the particles increases, and as a result all the fines and submicron size particles are collected much faster, for example 14 hours as opposed to 2 hours, and more efficiently. Thereafter, heating the aggregates, for example, from about 5.degree. C. to about 80.degree. C. above the resin Tg fuses the aggregated particles or coalesces the particles to enable the formation of toner composites of modified polyester polymer, pigments and optional toner additives like charge control agents, and the like, such as waxes. Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by charge neutralization while shearing, and thereby forming statically bounded aggregate particles by stirring and heating below the resin Tg; and thereafter, that is when the aggregates are formed, heating above the resin Tg to form stable toner composite particles. Of importance with respect to the processes of the present invention in embodiments is computer controlling the temperature of the heating to form the aggregates since the temperature can affect the rate of aggregation, the size of the aggregates and the particle size distribution of the aggregates. More specifically, the formation of aggregates is much faster, for example 6 to 7 times, when the temperature is 20.degree. C. higher than room temperature, about 25.degree. C., and the size of the aggregated particles, from 2.5 to 6 microns, increases with an increase in temperature. Also, an increase in the temperature of heating from room temperature to 45.degree. C. improves the particle size distribution, for example with an increase in temperature below the resin Tg, the particle size distribution, believed due to the faster collection of submicron particles, improves significantly. The latex blend or emulsion is comprised of resin or polymer, counterionic surfactant, and nonionic surfactant.
In reprographic technologies, such as xerographic and ionographic devices, toners with average volume diameter particle sizes of from about 9 microns to about 20 microns are effectively utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090 copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with, for example, an average volume particle of from about 2 to about 11 microns and preferably less than about 7 microns, and with narrow geometric size distribution (GSD) of from about 1.16 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized, such as pictorial color applications, small particle size colored toners, preferably of from about 3 to about 9 microns, are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130.degree. to 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present, such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing can be reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step can inhibit the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. Furthermore, toners with low minimum fixing temperature are desired to, for example, reduce the energy requirements of the printers and copiers, and to further extend the lifetime of the fuser rolls. In addition, nonvinyl offset properties and low relative humidity sensitivity are needed for toners. For certain xerographic properties, such as low minimum fixing temperature, nonvinyl offset characteristics, and high gloss properties, polyester resins, are known to be advantageous in comparison to styrene based resins. In contrast, styrene based toner resins are advantages in comparison to polyester resin for certain properties such as low relative humidity sensitivity, high blocking temperatures and in unit manufacturing cost.
These and other advantages are attained with the toners and processes of the present invention, and more specifically, by designing toner compositions comprised of both a polyester resin and styrene based resin, wherein the styrene base resin encapsulates the polyester resin such that the surface characteristics of the toner are directed by the encapsulant component, such as polystyrene-acrylic acid, and which encapsulant is responsible for the toners excellent blocking temperatures, triboelectric characteristics and RH-sensitivity provided by the acid residual, and wherein the core is comprised of a polyester which possesses a low minimum fixing temperature, such as from about 125.degree. C. to about 145.degree. C., high gloss properties, such as from about 40 to about 80 gloss units as measured by the Garner gloss metering unit, and excellent nonvinyl offset performance. These toner compositions can be prepared by emulsion aggregation and coalescence process resulting in small toner particle sizes, such as from about 1 to 7 microns, with narrow size distribution such as from about 1.15 to about 1.3 and high yields such as from about 97 to about 100 percent by weight, and with higher pigment loading such as from about 5 to about 12 percent by weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer on paper after fusing, thereby minimizing or avoiding paper curling.
Toners prepared in accordance with the present invention enable in embodiments the use of lower image fusing temperatures, such as from about 120.degree. C. to about 150.degree. C., thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, when a low gloss image of preferably from about 1 to about 30 gloss is desired, low gloss paper is utilized, such as from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and which after image formation with small particle size toners, preferably of from about 3 to about 5 microns, and fixing thereafter results in a low gloss toner image of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, when higher image gloss is desired, such as from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized, such as from about 30 to about 60 gloss units, and which after image formation with small particle size toners of the present invention of preferably from about 3 to about 5 microns, and fixing thereafter results in a higher gloss toner image of from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit. The aforementioned toner to paper matching can be attained with small particle size toners such as less than 7 microns and preferably less than 5 microns, such as from about 1 to about 4 microns, whereby the pile height of the toner layer or layers is considered low and acceptable.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 9 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In these processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields can be obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of, for example, from about 3 microns to about 9, and preferably 5 microns, are attained without resorting to classification processes, and wherein narrow geometric size distributions are attained, such as from about 1.16 to about 1.30, and preferably from about 1.16 to about 1.25. High toner yields are also attained, such as from about 90 percent to about 98 percent, in embodiments of the present invention. In addition, by the toner particle preparation process of the present invention in embodiments, small particle size toners of from about 3 microns to about 7 microns can be economically prepared in high yields, such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients, such as toner resin and pigment.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, however, the emulsion particles are not comprised of a polyester core with styrene-acrylic acid shell. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate, which results in the formation of particles with a wide GSD. Furthermore, the '488 patent does not, it appears, disclose the use of emulsion particles comprised of polyester core with styrene-acrylic acid shell.
Other prior art that may be of interest includes U.S. Pat. Nos. 3,674,736; 4,137,188 and 5,066,560.
Moreover, there is disclosed in U.S. Pat. No. 5,302,486, encapsulated toner composition comprised of a core and shell thereover, wherein these toners are prepared by a process which comprises microsuspending a mixture of a pigment, an organic phase such as a polyester resin A, and an olefinic monomer which after heating is polymerized to resin B, and wherein the incompatible resin A and resin B phase separate to whereby a core and shell results. However, with this microsuspension process, every toner particle is comprised of a shell encapsulating a core, whereas in the present invention, the toner particles are comprised of a multitude of smaller emulsion particles comprised of a shell and core, and wherein the shell material is coalesced to form the intact particle as illustrated therein, and which provide excellent pigment dispersion. Furthermore, the process of the present invention does not comprise a free-radical polymerization step as does the 486 patent, where it is known to adversely affect changes in color pigmentation due to the reaction of a radical and pigment.
The process described in the present application has several advantages as indicated herein including in embodiments the effective preparation of small toner particles with narrow particle size distribution as a result of no classification with high yields of toner, and which toners are comprised of pigment and coalesced particles of polyester core with styrene acrylic acid shell resulting in marking materials with superior performances such as nonvinyl offset, low minimum fusing temperature, excellent blocking and low relative humidity.